The present invention relates to a seat-back frame, and more particularly, to a seat-back frame including an upper-frame portion, two side-frame portions, a lower-frame portion, and a crosspiece arranged between the side-frame portions and having substantially a rectangular shape.
Conventionally, vehicle seat backs include a substantially rectangular pipe frame or panel frame, which is obtained by bending a pipe or a panel. In the case of the pipe frame, a spring member such as an S-shaped spring is arranged with the pipe frame, which is covered with a pad and a skin. Moreover, a hinge such as an armrest, a reclining device, etc. are fixed to the pipe frame by means of welding or the like.
The seat-back frame includes an upper-frame portion and two side-frame portions, having substantially an inverted-U shape. A lower-frame portion is arranged between lower ends of the side-frame portions. A one-side locking mechanism of the reclining device, etc. are mounted to the lower end of the side-frame portion. In view of an impact load that may be applied to the seat back in the lateral or longitudinal direction in the event of side or rear crash, the seat-back frame needs to have certain static and torsional rigidities. Thus, a reinforcing crosspiece is arranged between the side-frame portions.
However, the seat-back frame including a substantially rectangular pipe frame is excellent in static rigidity, but poor in impact absorption. On the other hand, the seat-back frame including a panel frame is poor in crash strength, since the side-frame portions may largely be deformed in the event of rear or side crash, i.e. they have greater deformation for impact absorption.
Moreover, the seat-back frame including a crosspiece is improved in rigidity, but complicated in assemblage, which increases manufacturing cost, resulting in poor cost efficiency. If the crosspiece is arranged adjacent to the lower-frame portion, the seat-back frame is excellent in static rigidity, but poor in torsional rigidity in the event of rear or side crash. On the other hand, if the crosspiece is arranged too away from the lower-frame portion, the seat-back frame is poor in both static and torsional rigidities.
It is, therefore, an object of the present invention to provide a seat-back frame that is excellent not only in static and torsional rigidities, but in cost efficiency.